Guided radiation receiver assembly and a radiation delivery waveguide for use therewith

ABSTRACT

A transparent radiation delivery waveguide and a guided radiation receiver assembly using the same, which assembly comprises a first transparent medium with a first refractive index n 1 , a receiver chamber having an aperture and holding a second transparent medium having a second refractive index n 2 , and the transparent radiation delivery waveguide having a third refractive index n 3  substantially equal or greater than n 1 . The radiation delivery waveguide n 3  consists of a transparent vessel holding a transparent liquid medium and has a first radiation intake portion in optical contact with the first transparent medium and held tightly within the aperture of the receiver chamber, and a second, tapered radiation delivery portion of non-circular cross-sectional shape, projecting into the receiver chamber.

This application is a Continuation-in-Part of application Ser. No.08/727,458, filed Oct. 18, 1996, now U.S. Pat. No. 5,796,892 as a 371 ofPCT/US95/04915, filed Apr. 20, 1995.

FIELD OF THE INVENTION

The invention relates to a waveguide for the transmission of guidedradiation from a medium with a high refraction index to a medium with alower refraction index. The waveguide according to the invention is inparticular suitable for the delivery of concentrated sunlight into asolar receiver, but may also be used in radio telescopes, fiber opticswaveguides and the like.

BACKGROUND OF THE INVENTION

A radiation delivery waveguide of the kind to which the presentinvention refers is, inter alia, described in PCT/US95/04915, the entiredisclosure of which is incorporated herein by reference.

The radiation delivery waveguide described in PCT/US95/04915 is used ina guided radiation receiver assembly comprising a first transparentmedium with a first refraction index n₁ and a receiver chamber having anaperture and holding a second transparent medium having a secondrefraction index n₂. The waveguide is transparent and has a thirdrefraction index n₃ substantially equal to or greater than n₁. Thetransparent radiation delivery waveguide has a first, radiation intakeportion in optical contact with the first transparent medium and heldtightly within the aperture, and a second tapered radiation deliveryportion of non-circular cross-sectional shape, projecting into thereceiver chamber.

Due to the specific design of the above radiation delivery waveguide,total and Fresnel reflections of the transmitted radiation at thewaveguide/second transparent medium boundary inside the receiver chamberare minimized and extraction of the delivered radiation is maximized.

The radiation delivery waveguide described above is particularlyadvantageous for use in the field of solar energy transfer, specificallyfor transferring concentrated radiation from optical concentrationsystems to a solar receiver. In this case, the radiation deliverywaveguide as well as the concentrator constituting the first transparentmedium, is made of a solid transparent medium, particularly of fusedsilica. However, calculations show that with large scale solar energysystems and, consequently, large scale receivers, the radiation deliverywaveguide will have such dimensions that if made of solid transparentmaterial it will be extremely heavy and expensive.

It is accordingly the object of the present invention to provide animproved, less expensive radiation delivery waveguide, and a radiationdelivery assembly using such a waveguide.

SUMMARY OF THE INVENTION

In accordance with the invention there is provided a guided radiationreceiver assembly comprising a first transparent medium with a firstrefraction index n₁, a receiver chamber having an aperture and holding asecond transparent medium having a second refraction index n₂, and atransparent radiation delivery waveguide having a third refraction indexn₃ substantially equal to or greater than n₁, which transparentradiation delivery waveguide has a first, radiation intake portion inoptical contact with said first transparent medium and held tightlywithin said aperture, and a second, tapered radiation delivery portionof non-circular cross-sectional shape, projecting into the receiverchamber, wherein said radiation delivery waveguide consists of atransparent vessel holding a transparent liquid medium.

In accordance with the present invention, for the purposes of lightextraction, the refraction index n₃ is that of the vessel.

The invention further provides a radiation delivery waveguide having atapered radiation delivery portion of non-circular cross-sectional shapecomprising a transparent housing holding a transparent liquid medium.

By one embodiment, the first transparent medium is a solar lightconcentrator made integral with said waveguide. In such an embodimentthe radiation delivery waveguide and concentrator preferably formtogether a single vessel holding a single body of transparent liquidmedium.

If desired, the radiation delivery waveguide may be linked to a heatexchanger for heat withdrawal from the transparent liquid mediumtherein.

The vessel of the radiation delivery waveguide according to theinvention may be of any suitable radiation-resistant material, e.g.fused silica. Due to the relatively small width of the vessel walls andthe relatively low density and price of the transparent liquid medium ascompared to fused silica or similar materials, the radiation deliveryguide in accordance with the present invention is of a relatively lowweight and inexpensive.

Furthermore, in accordance with the invention the radiation deliveryportion of the waveguide may hold additional elements made oftransparent material having an index of refraction different from thatof the liquid so as to interfere with a generally circular manner ofradiation propagation inside the radiation delivery waveguide andthereby allow for a more effective light extraction into the receiver.Such elements may be in the form of transparent solid rods orcylindrical hollow components, either empty or filled with liquid.

BRIEF DESCRIPTION OF THE DRAWINGS

For better understanding the invention will now be described, by way ofexample only, with reference to the annexed drawing which shows across-sectional view of a radiation receiving assembly according to theinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An assembly for receiving a concentrated radiation, shown in the drawingcomprises a receiver chamber 1 with a circular aperture 2 holding atransparent radiation delivery waveguide 3 having a first, cylindricalintake section 4 and a second, tapered radiation delivery section 5 of anon-circular cross-sectional shape. Intake section 4 fits snugly intoaperture 2 and is integral with a tubular concentrator 6. The walls 7 ofreceiver chamber 1 are transparent and they are surrounded by a solarabsorber body 8.

It should be noted that the shape of the radiation delivery waveguideaccording to the present invention, the construction of the radiationreceiver assembly, the mechanism of radiation delivery to the waveguideand radiation extraction from the latter to the receiver chamber, areessentially the same as described in PCT/US95/04915.

In accordance with the present invention, the radiation deliverywaveguide 3 and concentrator 6 are in the form of a single transparentvessel 9 holding a single body of transparent liquid medium 10. Thevessel 9 is made of solid material, e.g. quartz which is stable to longlight exposure. The vessel of the radiation delivery waveguide accordingto the invention may be of any other suitable radiation-resistantmaterial. Due to the relatively small width of the vessel walls and therelatively low density and price of the transparent liquid medium ascompared to fused silica or similar materials, the radiation deliverywaveguide in accordance with the present invention is of a relativelylow weight and inexpensive.

The liquid medium 10 may, for example, be an organic fluid having arefraction index of 1.33 to 1.6, such as a fluorinated saturatedhydrocarbon. Saturated fluorinated hydrocarbons are transparent in thenear UV spectral range and enable elimination of vibrational andovertone absorption in the visible and IR spectral ranges, as a resultof replacement of C—H bonds by C—F bonds. Alternatively, the liquidmedium may be a molten inorganic salt. If desired, the liquid medium ofthe delivery waveguide and concentrator may be replaced from time totime.

The radiation delivery portion of the waveguide, according to thepresent invention, may hold additional elements made of transparentmaterial having an index of refraction different from that of the liquidso as to interfere with a generally circular manner of radiationpropagation inside the radiation delivery waveguide and thereby allowfor a more effective light extraction into the receiver. Such elementsmay be in the form of transparent solid rods or cylindrical hollowcomponents, either empty or filled with liquid.

In a particular embodiment of the invention the radiation receiverassembly is part of a solar energy plant and the receiver chamber eitherholds directly an energy conversion device such as a solar radiationabsorber, a light/electricity transducer, a chemical reactor and thelike; or else is made of transparent walls with any such energyconversion devices on the outside. However, it should be noted that thepresent invention may be used quite generally in cases where it isrequired to extract radiation from a transparent element made of amaterial with a high refraction index, into a transparent element havinga lower index of refraction, and where the controllable, particularlyhigh, power density is required.

What is claimed is:
 1. A guided radiation receiver assembly comprising afirst transparent medium with a first refraction index n₁, a receiverchamber having an aperture and holding a second transparent mediumhaving a second refraction index n₂, and a transparent radiationdelivery waveguide having a third refraction index n₃ substantiallyequal to or greater than n₁, which transparent radiation deliverywaveguide has a first, radiation intake portion in optical contact withsaid first transparent medium and held tightly within said aperture, anda second, tapered radiation delivery portion of non-circularcross-sectional shape, projecting into the receiver chamber, whereinsaid radiation delivery waveguide consists of a transparent vesselholding a transparent liquid medium.
 2. A guided radiation receiverassembly according to claim 1, wherein said radiation delivery waveguideis linked to a heat exchanger for the withdrawal of heat from the liquidmedium therein.
 3. A radiation delivery waveguide having a taperedradiation delivery portion of a non-circular cross-sectional shapecomprising a transparent housing holding a transparent liquid medium. 4.A radiation delivery waveguide according to claim 3, made integral witha radiation concentrator.
 5. A radiation delivery waveguide according toclaim 4, comprising a single vessel with radiation delivery andconcentrator sections holding a single body of transparent liquidmedium.
 6. A radiation delivery waveguide according to claim 5, whereinthe vessel holds additional elements of transparent material having anindex of refraction different from that of the liquid.
 7. A radiationwaveguide according to claim 3, adapted for being linked to a heatexchanger for heat withdrawal from the liquid medium therein.